The present invention relates to turbomachines, such as blowers, compressors, pumps and fans of the axial, semi-axial and radial type. The working medium may be gaseous or liquid.
More particularly, this invention relates to a turbomachine with at least one rotor, with the rotor comprising several rotor blades attached to a rotating shaft. At least one stator can exist, with the stator being provided with stationary stator blades. A casing can exist which confines the passage of fluid through the rotor and the stator in the outward direction.
The aerodynamic loadability and the efficiency of turbomachines, for example blowers, compressors, pumps and fans, is limited by the growth and the separation of boundary layers on the blades as well as on the hub and casing walls.
To remedy this fundamental problem, the state of the art proposes that the boundary layer of the fluid be removed. Apart from this very general provision, the known solutions are trivial and only partially effective.
FIGS. 1 and 2 schematically show the solutions known from the state of the art. Here, FIG. 1 schematically shows a casing 1 and a hub 11 between which a fluid flow passes from the left-hand side, as indicated by the big arrow. Reference numeral 2 schematically shows a blade, with the visible area of this blade being the “suction side”. As indicated by the upward arrows of FIG. 1, air is locally removed on the blade suction side and in the axial gap in axially symmetric arrangement. The downward, left-hand arrow shows a removal of air on a rotor or stator via a circumferential slot 3 before the blade. Reference numeral 4 shows a solution in which air is removed via a slot on a stator and via a perforation, a slot, holes or a ramming inlet on a rotor.
The upward arrow in FIG. 2 shows global removal of air via porous blade surfaces. Reference numeral 5 designates a stator in a fine-pore, sweating material.
The state of the art accordingly describes various methods for pointwise removal of the boundary layer in flow direction via slots or holes on the blade suction side or via axially symmetric slots on the sidewalls (hub, casing) before the blade. Also, as already mentioned, the removal of air by way of global boundary layer suction distributed over the entire blade surface by way of fine-pore material has been proposed for stators.
The measures described either are not specifically geared to aerodynamically particularly problematic zones within the blade passage or are simply orientated to a two-dimensional profile envelopment, without considering the complex, three-dimensional aerodynamic processes in the side wall area of a blade (near a hub or on a casing).
Normally, in the state of the art, the boundary layer is initially led to the blade interior and is then discharged from the blade and the annulus of the turbomachine.
Only one solution provides for suction of the boundary layer on the suction side of a blade and its direct return at the tip of the same blade.
Furthermore, drafts exist in the state of the art that provide circumferential slots before or behind a blade row on a hub or a casing to suck off the side wall boundary layer there. This measure is solely aimed at the reduction of the boundary layer thickness at the blade entry, without being specifically geared to particularly problematic side wall zones within the blade passage.
The above state of the art is documented in writing in the following publications.
For boundary layer suction on the blade surface via holes, individual slots or porous zones, reference is made to the following U.S. patents:                U.S. Pat. No. 2,870,957        U.S. Pat. No. 2,720,356        U.S. Pat. No. 3,694,102        U.S. Pat. No. 3,993,414        U.S. Pat. No. 5,904,470        U.S. Pat. No. 5,480,284        
For boundary layer suction on the hub or on the casing via circumferential slots before or behind the blade row, reference is made to the following Publications:                Schuler et al.: Design, Analysis, Fabrication and Test of an Aspirated Fan Stage, ASME Paper 2000-GT-618, and        Merchant et al.: Aerodynamic Design and Analysis of a High Pressure Ratio Aspirated Compressor Stage, ASME Paper 2000-GT-619.        
In the state of the art, it is disadvantageous that the existing solutions are not highly effective and, in particular, are unfavorable with regard to the efficiency of the turbomachinery. Rather, the existing suction concepts are relatively primitive and provide for suction of the profile boundary layers either only on the blade surface or in combination with suction before the blade row via axially symmetric annular slots on the hub or casing.